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Materials And Hardware > Metals, Crystals, Processes > Flashcards

Metals, Crystals, Processes Flashcards

1
Q

What three lightweight metals are used in aircraft?

A

Aluminium and Aluminium Alloys
Titanium and Titanium Alloys
Magnesium and Magnesium Alloys

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2
Q

What is the basic building block of a crystal called?

A

Unit Cell

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3
Q

How do Unit Cells form a crystal?

A

Repetition

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4
Q

Three types of crystals and their amount of atoms?

A

BCC - Body Centred Cubic - 9 Atoms
FCC - Face Centred Cubic - 14 Atoms
HCP - Hexagonal Close Packed - 17 Atoms

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5
Q

What is a Ferrous metal?

A

Contains iron

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6
Q

What is a Non-Ferrous metal?

A

Doesn’t contain iron

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7
Q

Steel Characteristics, Properties, and Identification

A

Base material is iron
Alloyed primarily with carbon
Molten iron alloyed with less than 2% carbon and poured into a mould
Cast iron is formed

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8
Q

How to make steel?

A

Pure iron is remelted in a special furnace where carbon is introduced along with other alloying elements to achieve the desired characteristics

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9
Q

What does Carbon do?

A

Primary hardening, permits heat treatment

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10
Q

Low Carbon Steels…

A

0.1% - 0.3% carbon

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11
Q

Medium Carbon Steels…

A

0.3% - 0.5% carbon

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12
Q

High Carbon Steels…

A

0.5% - 1.05% carbon

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13
Q

What does Sulphur do?

A

Normally kept low, decreases ductility

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14
Q

What does Phosphorous do?

A

Strength, hardness, corrosion resistance

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15
Q

What does Nickel do?

A

Hardenability and impact strength

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16
Q

What does Chromium do?

A

Corrosion resistance, high temperature strength

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17
Q

What does Molybdenum do?

A

Impact strength, creep strength

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18
Q

What does Vanadium do?

A

Tensile strength, yield strength

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19
Q

What does Titanium do?

A

Toughness

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20
Q

What are the Alloying Ingredients for Steel?

A 
Carbon 
Sulphur 
Phosphorus 
Nickel 
Chromium 
Molybdenum
Vanadium 
Titanium
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21
Q

What is a material designation?

A

Four digit code, first two denoting the steel and what Alloys have been used, the last two denotes the percentage of carbon (AISI or SAE numbers)

SAE 1030 (1 carbon steel, 0 plain carbon steel, 0.3% carbon)

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22
Q

What is Tempering?

A

Method used to decrease the hardness, thereby increasing the ductility and toughness of the quenched steel. Quenching produces stresses - tempering relieves these stresses

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23
Q

How to Harden Steel

A

Heated above it’s critical temperature, allowing carbon to disperse in the iron matrix

The alloy is then cooled rapidly by quenching it in water, oil, or brine

If the quench is too quick, the structure becomes martensitic (the hardness it could possibly be - too brittle for use on aircraft)

24
Q

Which product gives the strongest quench?

A

Brine

25
Q

What is Annealing?

A

Softens and relieves internal stresses

26
Q

How to carry out Annealing

A

Heated to Upper Critical Limit + 50F

Soaked at this temperature

Cooled very slowly at room temperature

Results in very soft and ductile metal

27
Q

Which process results in a very soft and ductile metal?

A

Annealing

28
Q

How to carry out Normalising

A

Heat steal to 100 degrees F above its Upper Critical Limit

Soak for prescribed time

Cool at room temperature

29
Q

What is Quenching?

A

The rate steel will cool down when quenched is governed by the quenching medium

30
Q

What is Ferrite?

A

Pure iron

31
Q

What is Austenite?

A

Can absorb more carbon (up to 2%)

32
Q

What is Cementite?

A

Very very hard compound made of iron and carbon

33
Q

What is Pearlite?

A

Structure composed of alternating layers of Ferrite and Cementite

34
Q

What does CRES stand for?

A

Corrosion Resistant Stainless Steel

35
Q

What is CRES?

A

Strength and toughness and resistance to high temperature

Identified by a three digit system 200,300,400

200 and 300 known as Austenitic

400 known as Ferrite

300 is the most common in aircraft use

36
Q

Disadvantages of CRES

A

Difficult to cut

Greater coefficient of expansion

Not suitable in high temp environments (engines)

Experienced technician needed

37
Q

What is Austenitic?

A

Chromium/Nickel and chromium nickel manganese alloy.

Face centred cube

18% or more carbon

3.5% - 22% nickel

Contains stabilising alloys

200/300 series

Cold worked/strain hardened

Non-magnetic

38
Q

What is Ferritic?

A

Body centred cubic

400 series

15%-30% chromium

Small amounts of aluminium

Non-heat treatable (no Carbon)

Magnetic

39
Q

What is Martensitic?

A

400 series

12%-18% chromium

High carbon content

Heat treatable

Least corrosion resistant

40
Q

What is Precipitation Hardening?

A

Little carbon

15%-17% chromium

4%-7% nickel

Solution heat treated

Can be hardened to very high strengths

Excellent corrosion resistance

41
Q

What is High Strength Low Alloy Steel?

A

Iron based alloys

Can be hardened to very high strengths

High strength alloy 300M used on landing gear

42
Q

What is Hydrogen Embrittlement?

A

Phenomenon that occurs in Ferrous and Titanium alloys

The hydrogen migrated to an area such as the grain boundaries or voids in the metal. At high temperatures, hydrogen concentrations react with carbon to form methane which causes a build up of pressure that can cause cracks.

43
Q

Name Steel Alloys Rework Precautions

A

Stress concentrations: Misuse of tools leading to scratches, general damage to surface finish, etc

Hydrogen embrittlement: Ensure all precautions are taken to prevent embrittlement

44
Q

Name some Surface Protection

A

CRES doesn’t normally require protective treatment. Cadmium plated, zinc sprayed or chromate will prevent galvanic corrosion on light alloys.

Non Stainless Protection: 
Cadmium 
Paint
Aluminium spray 
Chromium and Nickel plating 
Silver playing (not when in contact with Aluminium)
45
Q

What is Galvanic Corrosion?

A

Galvanic Corrosion potential is a measure of how dissimilar metals will corrode when placed against each other in an assembly

46
Q

What is Case Hardening?

A

Gives steel components a hard, durable surface that is suitable for load bearing whilst retaining a tough core

Not suitable for non-ferrous materials

47
Q

What is Carburising?

A

Produces a thin layer of high carbon steel on the surface of a low carbon steel component

Heat metal to 900C while in contact with carbon-rich medium. Followed by suitable heat treatment

48
Q

Three types of Carburising?

A

Pack
Gas
Liquid

49
Q

What is Pack Carburising?

A

Heating a component up to temperatures of 1700F whilst it is packed into a carbon-rich material such as charcoal. Carbon penetrates the surface of metal causing it to harden

Metal then quenched in oil

50
Q

What is Gas Carburising?

A

Object placed in basket in a furnace, through which a suitable carbon-rich gas is passed (e.g methane)

51
Q

What is Liquid Carburising?

A

Object heated to a suitable temperature and immersed in a hot salt bath at 900C

52
Q

What is Flame Hardening?

A

Surface heated to above Upper Temperature by an oxyacetylene torch and immediately quenched with a jet of water

53
Q

What is Induction Hardening?

A

Similar to flame hardening, but the whole circumference is heated simultaneously by an induction coil

54
Q

What is Nitriding?

A

Produces an improved final surface finish compared to carburising as the component is hardened, tempered, and ground to its final dimensions prior to surface hardening

55
Q

What is Hardening?

A

Involves heating the material to 1000F in an Ammonia-rich environment. The ammonia breaks down, alloying the nitrogen to penetrate the surface. Special alloys, known as Nitroalloys, are used in the manufacture of compounds that are going to be used in the nitriding process

Materials And Hardware (11 decks)

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